Update marker test to use Python 3.6 instead of 2.6
Update marker test to use Python 3.6 instead of 2.6

pradyunsg/pip,xavfernandez/pip,pradyunsg/pip,pypa/pip,rouge8/pip,pfmoore/pip,rouge8/pip,pfmoore/pip,rouge8/pip,pypa/pip,sbidoul/pip,sbidoul/pip,xavfernandez/pip,xavfernandez/pip